The present invention relates to a sealed, evacuatable crucible for inductive melting or superheating of metals, alloys or other electrically conductive materials, having a plurality of palisades which are arranged vertically and parallel to one another and distributed on an arc of a circle and distanced from one another, which enclose the melt and form the crucible wall, and having a base part which forms the base of the crucible and carries the palisades, wherein the palisades are provided at least in part with voids through which there flows a cooling medium, and having an induction coil which is wound round the palisades from outside in direct manner distanced therefrom, and through which there flows an alternating current.
There is known a process for melting difficultly meltable metals, in particular tantalum, tungsten, thorium or alloys thereof, in a water-cooled vessel (DE 518 499), wherein the vessel is made of substances having a melting point lower than that of the charge material, for example of quartz glass, copper or silver, and the energy necessary for melting is supplied and the vessel cooled such that the charge material is melted-down in residue-free manner without impurities arising from the crucible material. The actual crucible is heatable with the aid of an induction coil, wherein a circulating crucible current is prevented by the composition thereof from individual segments which are separated from one another by an isolation layer, for example of mica.
There is also known a high-frequency induction crucible formed of a plurality of palisades which are all arranged in a vertical manner on a disk-shaped base plate together forming a hollow cylinder (U.S. Pat. No. 3,461,215). Cooling water flows through all the current-conducting and heat-conducting palisades around which there is wound an induction coil. The base plate of ceramic material is provided with a closure by way of which the melt may be removed. Strips of isolating material are inserted between the palisades.
There is furthermore also known a crucible for slag-free melting of high-purity reactive metals in a vacuum chamber (EP 0 276 544), in which cooling water flows through the palisades around which the induction coil is wound in uniting manner and which are bolted firmly to a disk-shaped base plate, wherein the tubular palisades on the one hand are separated from one another by slots and, on the other, are all connected with one another in electrically conductive manner by way of the base plate which is formed of metal.
There is also known a liquid-cooled crucible, the wall of which is formed by metal tubes having high electrical and thermal conductivity and which is arranged for melting the charge material in the high-frequency field of an induction coil (DE-OS 1 946 735). The crucible wall consists of tube sections arranged parallel and adjacent to one another, some of which have parts which re-enter the interior of the crucible and form the crucible base. The distance dimensioned between the tubes is so small that the molten charge material cannot pass through the crucible wall. The crucible base has an opening which is delimited by the tube end sections which form the crucible base and is so narrow that solid charge material cannot pass through, and that a centering ring surrounds the opening. The actual crucible is encompassed by a quartz tube, the lower end of which is closed by a bottom plate and the upper end by a platform in the region of the crucible opening, wherein there is provided a further chamber with which the charge opening of the crucible is closable. Below the opening in the crucible base there is provided a vessel which serves to receive the molten charge.
There is furthermore known an induction melting apparatus for the melting of high-melting reactive metals, which is sealed to the atmosphere, and has a connection to connect it to a source of negative pressure or an inert gas source (DE-OS 42 28 402). This apparatus has an unlined melting crucible of metal around which there is wound an induction source, and a casting mould arranged below the melting crucible below an outlet. The melting crucible has a lid which hermetically closes the latter and a downwardly directed jacket-form extension in which the casting mould is arranged in sealing relationship to the internal jacket surface of the extension.
There is known, finally, a process for melting refractory metals such as, for example, titanium or zirconium (U.S. Pat. No. 2,825,641), in which the water-cooled crucible is provided on the base part thereof with a discharge opening which is closable with the aid of a cooled stopper rod, for which purpose the stopper rod is positioned in the wall of a chamber arranged below the crucible and is activatable externally by means of a handle.
An object of the present invention is to provide a crucible of the type under consideration, which suffices without isolating slag material, in which energy losses reduced, and non-productive times necessitated by carrying out the melting and casting operation are as short as possible.